An image processor well known in the art for generating image data representing an image to be formed on a printer or other image-forming device first generates image data having a higher resolution than the resolution at which the image-forming device can actually form images, and subsequently performs anti-aliasing to convert the image data to a resolution that the image-forming device supports. For example, when the image-forming device can form images at a resolution of 100 dpi, a conventional image processor first generates image data at 200 dpi and subsequently converts the image data to 100 dpi through a reduction process for converting every four pixels of the 200 dpi image data to one pixel. The value of the pixel resulting from the reduction process is calculated by averaging the values of the four pixels in the original image data. Through this reduction process, pixels in edge portions of characters, graphics, and the like are converted to intermediate values by combining the values of pixels in edge parts with the values of pixels in the background prior to the reduction process, thereby producing edges that appear smooth without a noticeable jagged look.